To the best of my knowledge there is no written standard for solder mask/conformal coating compatability, but I have heard instances where poor adhesion of conformal coating to the solder mask was preceived as a problem. It's a dirty little secret that not all conformal coatings adhere to all solder masks; I've seen some that peel right off, no matter how clean the underling solder mask is.

At one time Enthione had a flier listing the "compatability" of popular conformal coatings to their solder masks. THer criteria that they used to judge this was vague. I don't know if it's still available.

HumiSeal tried to develop a correlation between the surface tensions of conformal coatings and solder masks to predict adhesion but was unsuccessful.

1B31S - a goosed up version of 1B31-  has improved adhesion to some problem solder masks, but there are still some solder masks where 1B31S will  peel right off.

Doug Pauls is correct that cleaning problems are sometimes mistaken for incompatabilty of solder masks to conformal coating. Frequently this was solder mask batch related, sometimes process, sometimes the chemistry of the batch itself.

Somewhere IPC (IPC-CC-830?) calls out an adhesion test for conformal coating to solder masks. The test cuts a grid larger than 1" X 1" into the coating with a $100 plus apparatus and then trys to lift off coating squares with tape. That test is  operator dependent (subjective) and it's hard to find a 1" square area free of components on most boards.



Edward Mines BEChE, MEChE
238 Willard Dr.
Hewlett, NY  11557
516 205-6523
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